A conventional foldable bicycle as shown in FIG. 8 adopts two plates (90), (91) to respectively connected two tubes (96, 97) of the frame of the bicycle, the two plates (90, 91) are pivotally connected with each other. The plate (90) has two rings (901) extending form one of two ends thereof and a bolt (93) has the head (931) thereof retained between the two rings (901). A quick release bar (95) has its actuating portion (951) rotatably inserted through the two rings (901) and the hole (930) defined through the head (931) so that when rotating the quick releaser bar (95), the bolt (93) is rotated toward the plate (91). The plate (91) has a notch (911) defined in one of two ends thereof so that the shank portion (932) of the bolt (93) is engaged with the notch (911) to let the two tubes (96, 97) be located in alignment with each other. The shank portion (932) is engaged with a nut (94) to fixedly position the bolt (93) relative to the plate (91). By the device, the bicycle frame can be folded. However, The notch (911) is an open notch and the shank portion (932) in the notch (911) is simply clamped by the nut (94) so that the shank portion (932) could disengage from the notch (911) if an unexpected impact is happened to the shank portion (932). This will result in a dangerous disaster.
The present invention intends to provide a pivotable device for pivotably connecting two parts of a foldable bicycle. The device has a clutch means and a secure means to ensure the two parts will not disengaged from each other so that the present invention mitigates the disadvantages of the conventional pivotable device for connecting two parts of a foldable bicycle.